Ultra-high luminance light-emitting devices are produced by successively growing a quaternary light-emitting layer and a light-extraction window layer on a GaAs substrate in a reactor using a Metal Organic Vapor Phase Epitaxy method (hereinafter, referred to as a MOVPE method), and growing a thicker window layer on the window layer after transferring the substrate into a reactor using a Hydride Vapor Phase Epitaxy method (hereinafter, referred to as a HVPE method), followed by performing processes such as electrode formation, and cutting it into individual chips through a dicing step, etc. Such a thickening of the window layer improves a light extraction efficiency from the side of the light-emitting device.
On the other hand, a light emitted from the light-emitting layer toward the substrate side is absorbed by the GaAs substrate. Accordingly, in order to improve the light extraction efficiency, the GaAs substrate is removed by etching to directly bond an epitaxial wafer in which the growth substrate is removed and a GaP substrate or a sapphire substrate, which is a transparent substrate, so as to prevent the foregoing absorption of light from the light emitting layer and so as to extract the light emitted from the light emitting layer toward the substrate side. Such a structure makes it possible to efficiently extract the light from the light emitting layer through the upper window layer and the transparent substrate which is bonded directly thereto.
In bonding by direct joining, however, a region having a void formed therein (a bonding failure part) is sometimes observed on the bonding interface. There are many automatic detectors using an optical system for detecting such a bonding failure part (for example, see Patent Document 1). In these detectors, however, an illumination light is irradiated from the horizontal direction or the upper diagonal direction, and the bonding failure part is detected on the basis of the difference of brightness (light and darkness) between the reflected-light from the bonding failure part and the reflected-light from the bonding good part.